Modern power generating stations or power plants use steam turbines to generate power. In a conventional power plant, steam generated in a boiler is fed to a turbine to where the steam expands as it turns the turbine to generate work to create electricity. Occasional maintenance and repair of the turbine system is required. During turbine maintenance periods or shutdown, the turbine is not operational. It is typically more economical to continue boiler operation during these maintenance periods, and as a result, the power plant is designed to allow the generated steam to continue circulation. In order to accommodate this design, the power plant commonly has supplemental piping and valves that circumvent the steam turbine and redirect the steam to a recovery circuit that reclaims the steam for further use. The supplemental piping is conventionally known as a Turbine Bypass.
In Turbine Bypass, steam that is routed away from the turbine must be recovered or returned to water. The recovery process allows that plant to conserve water and maintain a higher operating efficiency. An air-cooled condenser is often used to recover steam from the bypass loop and turbine-exhausted steam. To return the steam to water, a system must be designed to remove the heat of vaporization from the steam, thereby forcing it to condense. The air-cooled condenser facilitates heat removal by forcing low temperature air across a heat exchanger in which the steam circulates. The residual heat is transferred from the steam through the heat exchanger directly to the surrounding atmosphere. This recovery method is costly due to the expense of the air-cooled condenser. Consequently, certain design techniques are used to protect the air-cooled condenser.
One design consideration that must be addressed is the bypass steam's high operating pressure and high temperature. Because the bypass steam has not produced work through the turbine, its pressure and temperature is greater than the turbine-exhausted steam. As a result, bypass steam temperature and pressure must be conditioned or reduced prior to entering the air-cooled condenser to avoid damage. Cooling water is typically injected into the bypass steam to moderate the steam's temperature. The superheated bypass steam will generally consume the cooling water through evaporation as its temperature is lowered. However, this technique does not address the air-cooled condensers' pressure limitations. To control the steam pressure prior to entering the condenser, control valves and more specifically fluid pressure reductions devices, commonly referred to as spargers, are typically used. The spargers are aerodynamically restrictive devices that reduce pressure by transferring and absorbing fluid energy contained in the bypass steam. Typical spargers are constructed of a hollow housing which receives the bypass steam and a multitude of ports along the hollow walls of the housing providing fluid passageways to the exterior surface. By dividing the incoming fluid into progressively smaller, high velocity fluid jets, the sparger reduces the flow and the pressure of the incoming bypass steam and any residual spray water within acceptable limits prior to entering the air-cooled condenser.
Typical turbine bypass applications dump the bypass steam and residual spray water directly into large condenser ducts that feed the air-cooled condenser. In the process of reducing the incoming steam pressure, the spargers transfer the potential energy stored in the steam to kinetic energy. The kinetic energy generates turbulent fluid flow that creates unwanted physical vibrations in surrounding structures and undesirable aerodynamic noise. Additionally, the fluid jets, consisting of high velocity steam and residual spray water jets, exiting spargers can interact to substantially increase the aerodynamic noise.